1. Field of the Invention
The present invention relates to a gripper used in an automatic bag filling apparatus in which a plurality of pairs of grippers are provided at equal intervals around a periphery of a transportation member that rotates continuously or intermittently so that each pair of grippers grip two locations on either side edge of a gusset bag and is rotated along a predetermined circular path along with the transportation member.
2. Related Art
An intermittently rotating table type bag filling apparatus, for instance, is equipped with a table that rotates intermittently and a plurality of pairs of grippers that are installed around the periphery of the table at equal intervals and rotated intermittently together with the table. In this bag filling apparatus, during one rotation of the table, one gusset bag is supplied to the grippers, and the filling process that includes opening of the bag, filling of the bag with contents, and, if necessary, sealing of the bag mouth, is performed with the gusset bag being gripped at its both side edges by the grippers and hanged from the grippers.
An example of this type of bag filling apparatus gripper is disclosed in, for instance, Japanese Patent Application Laid-Open (Kokai) No. 2007-210645. This bag filling apparatus gripper includes grippers equipped with pairs of left and right gripper arms swingably mounted on an intermittently rotating table, chuck holders that are rotatably mounted on the gripper arms and make a translational motion (movement in parallel) upon the swing motion of the gripper arms so that the chuck holders narrow and widen the space in between, an inside chuck section and an outside chuck section which are respectively comprised of a fixed chuck element and a movable chuck element and provided to face each other at the tip end portion of each chuck holder, chuck open/close mechanisms that open and close the inside and outside chuck sections, and a chuck positioning mechanism that move the inside and outside chuck sections inwardly and outwardly between a close position and a separate position.
However, these grippers have several problems.                (1) Since the structure of the grippers, particularly the structure of the chuck open/close mechanism, is complex, this complexity increases the costs and makes cleaning and maintenance more difficult.        (2) When changing the position of process (bag supply, removal of filled bag and other processes) or adding process (a re-holding and weighing process) in which the chucks are opened and closed, a drive mechanism (chuck open/close bar) to activate the chuck open/close mechanism of the grippers in that process location must be installed; however, the drive mechanism therefor must be linked mechanically (via a cam or the like) to the main (i.e., rotating table) drive mechanism, and this makes design changes and/or modifications difficult.        (3) When the inside and outside chuck sections are moved apart from each other (so as to open the bag), the chucks cannot be released structure-wise, it is impossible to employ a re-holding and weighing process that requires opening and closing of the chucks.        (4) It is desirable to vary the gripping force of the chucks depending on the material and thickness of the bag and depending on the amount of material to be filled in the bag; however, it is extremely difficult to adjust the gripping force by a lock pin, and even the skilled technicians, it takes quite some time to do this.        
Japanese Utility Model Application Publication (Kokoku) No. H7-18571, Japanese Patent Application Laid-Open (Kokai) No. 2005-320012, and Japanese Utility Model Application Laid-Open (Kokai) No. S55-90506 disclose grippers that are installed around an intermittently rotating transportation member (table or endless chain). However, all of these grippers have the same problems as those of (1) and (2) described above. In addition, though it is desirable to change the gripping force of the chucks according to, for instance, the bag material and thickness and to the amount of material to be filled, the grippers of these three (3) relevant art provide the gripping force of the chucks by a spring bias force, and it is necessary to change the spring if the gripping force is desired to change. However, since a large number of springs (four for each gripper) are used, replacing the springs is extremely laborious and takes time even for the skilled technicians.